THE HYDROCARBON EMISSION RATES OF TEA-LEAFED WILLOW (SALIX PHYLICIFOLIA), SILVER BIRCH (BETULA-PENDULA) AND EUROPEAN ASPEN (POPULUS-TREMULA)

The monoterpene, isoprene, and light hydrocarbon emission rates of tea -leafed willow (Salix phylicifolia), aspen (Populus tremula), and silv er birch (Betula pendula) were measured during the growing season 1996 in the boreal vegetation zone using a dynamic flow-through technique. All tree species had significant (2.8-10 mu g g (dry weight)(-1) h(-1 )) monoterpene emission rates when leaves were young in May. In additi on, willow emitted l-butene, ethene, and propene when it was blooming in May. In August, silver birch emitted monoterpenes (6-12 mu g g (dry weight)(-1) h(-1)). Then the main species emitted were ocimenes and s abinene. Birch emitted only minor amounts of isoprene. Willow and aspe n are high isoprene emitters (up to 76 mu g g (dry weight)(-1) h(-1) i n August). Isoprene emissions began 2-3 weeks after onset of leafing. The phenological state was estimated using the effective temperature s um. Isoprene synthase began when the effective temperature sum exceede d 120-210 and 120-280 degree days for willow and aspen, respectively. In addition to phenology, isoprene emissions were dependent on tempera ture and photosynthetically active radiation while the terpene emissio ns were dependent on temperature only. (C) 1996 Elsevier Science Ltd. All rights reserved.